The present invention relates to a semiconductor device of a multilayered wiring structure, and more particularly to a semiconductor device in which a lower wiring layer is made of a material containing Al and upper and lower wiring layers are connected via a barrier metal film interposed therebetween.
In general, barrier metal films are formed above and below a wiring layer in a semiconductor device in order to protect the wiring layer and improve reliability. This matter is described in, for example, "Proceedings of 11th International VLSI Multilevel Interconnection Conference (1994)", pages 172 to 178.
A method for manufacturing a conventional semiconductor device having barrier metal films will be described with reference to FIGS. 23 and 24.
First, as shown in FIG. 23, an insulating film 101 is formed on a part or the main surface of an active area having source/drain regions and a gate on a silicon substrate. A Ti film 102, a TiN film 103, an AlCu film 104, a Ti film 105 and a TiN film 106 are formed in this order on the silicon substrate.
The AlCu film 104 constitutes a first wiring layer. The Ti film 102 and the TiN film 103 formed under the AlCu film 104 and the Ti film 105 and the TiN film 106 formed above it are used as barrier metal films of the wiring layer including the AlCu film 104.
The barrier metal films have a multilevel structure constituted by two layers, each including Ti and TiN films. The TiN film 106 of the upper barrier metal film is also used as anti-reflection layer for lithography. The Ti film 105 is also used to prevent the surface of the AlCu film 104 from being nitrided when the TiN film 106 is deposited.
Then, as shown in FIG. 24, an SiO.sub.2 film 107 serving as an interlayer insulating film is deposited on the main surface of the substrate. Thereafter, a resist pattern (not shown) is formed on the substrate by means of the lithography. Using the resist pattern as a mask, the SiO.sub.2 film is selectively etched by the RIE method. Subsequently, the resist pattern is removed, thereby forming a via 108.
Thereafter, a Ti film 110, a TiN film 111, and an AlCu film 109 to be a wiring material, are deposited on the main surface and then patterned. As a result, a second wiring layer 109, electrically connected to the AlCu film 104, is formed.
In the conventional method described above, after annealing at 450.degree. for 60 minutes, a sheet resistance of a wiring layer including an AlCu film 104 was increased to about 0.45 (.OMEGA./.quadrature.). Thus, the conventional method has a problem that an increase in wiring resistance must be suppressed. Further, it is desirable that the overall lower wiring layer including the upper and lower barrier metal films be thin.